The purpose of this project is to participate, as one of the many investigative centers, in all phases of the Coronary Drug Project, and to help accomplish its objectives as specified in the common protocol. The major objective of the Coronary Drug Project Cooperative study is to test the effectiveness of long term therapy with certain lipid-modifying drugs (Conjugated equine estrogens, Dextrothyroxine, Ethyl chlorphenoxyisobutyrate and Nicotinic acid) in reducing mortality and recurrent cardiovascular morbidity in middle aged males with a previous history of one or more myocardial infarctions. After admission to the study, such patients are randomised into a placebo group or one of the five treatment groups. Patients are then followed for five years or until death. By studying the control group as intensively as treatment groups the study also helps in gaining further information on the long term prognosis of myocardial infarction. Since the onset of the study data accumulated on the effects of 3 of the treatment regimens, Dextrothyroxine, High dose and Low dose estrogen, have indicated that these drugs are ineffective in prolonging life and have unacceptable toxicity. They have been discontinued and after a period without drug therapy the patients originally assigned to these regimens have been randomly and in a double blind fashion treated with aspirin or placebo to determine if this platelet aggregation inhibitor will effect prognosis.